The detonators were concealed in a bag of corn, an official at the ministry's information center said on condition of anonymity in line with policy.

He said police stopped the bus after a tip-off in Nochchiyagama of Anuradhapura district, about 160 kilometers (100 miles) northeast of Colombo.

Two passengers were arrested on suspicion they may have been transporting the devices for separatist Tamil Tiger rebels, he said.

The detection came a day after soldiers acting on another tip found five suicide bomb belts and several cyanide capsules among a haul of arms and explosives in a Tamil Tiger rebel hide-out in the northern Jaffna peninsula.

Military spokesman Brig. Prasad Samarasinghe said the mainly Tamil civilians in the peninsula were beginning to cooperate with the army instead of the rebels, who have been fighting for more than two decades to establish an ethnic Tamil homeland in north and east of Sri Lanka.

"Now the civilians are giving information to us because the civilians are not confidant in the LTTE," he said, referring to the Liberation Tigers of Tamil Eelam rebels.

The Tamil Tigers are blamed for carrying out more than 240 suicide bombings aimed at both military and civilian targets across the country.

Former Indian Prime Minister Rajiv Gandhi and former Sri Lankan President Ranasinghe Premadasa have been among the victims of rebel suicide bombers.

Minority Tamils, who have suffered decades of discrimination by the majority Sinhalese-controlled governments, consider Jaffna their cultural heartland. The military has controlled the region since 1995, but the rebels operate underground and carry out frequent assassinations and bomb attacks there.

A Norway-brokered cease-fire in 2002 brought relative calm to the country, but a new wave of violence that began in December 2005 has killed more than 5,000 people and displaced hundreds of thousands. Over 70,000 people have been killed in the two decades of violence.

Not that long ago, American soldiers would train their skills to counter insurgent and partisan military organizations. These days, they are trained to show resistance to the regular army of a potential adversary